Current belief in the field of dermatology is that patients with skin conditions such as acne or hyperhidrosis respond to a given treatment at a given dose proportionately to the severity of their illness. For example, consider the study of patients who have acne, the most prevalent of all skin diseases: If hypothetical Patient A has 100 acne lesions on her face and hypothetical Patient B has 50 lesions on her face and they each receive a 50 mg pill of Agent X that has been shown to be an effective treatment for acne, then if Patient A has 50% reduction in the number of acne lesions (which in her case would be a reduction by 50 lesions) it would be expected that Patient B would have approximately a 50% reduction in acne lesions (which in her case would a reduction by 25 lesions). This assumption enables the comparison of patients within a study despite different patients being enrolled in the study with different levels of baseline disease severity. This assumption essentially “normalizes” changes in disease state due to treatment by reference to each patient's own baseline of disease. This assumption not only enables the comparison of patients within a study despite different patients being enrolled in the study with different levels of baseline disease severity, but it also enables the comparison of results across studies of similar (e.g., one retinoid cream versus another) or different treatments (e.g., a retinoid cream versus an antibiotic cream) for acne. The different treatments can be compared across studies by comparing the percent reductions in acne lesions for each treatment/study. See Webster (2011), who summarizes dozens of standard acne treatment clinical studies that use percent reductions in acne lesions as study outcome measures; Webster then compares these study results against one another using this same percent reduction in acne lesions for differing treatments.
Similarly, consider hyperhidrosis, a condition that is characterized by excessive sweating and affects about 3% of the population (or approximately 10 million people in the United States): If hypothetical Patient A has underarm sweating of 200 mg in 5 minutes and hypothetical Patient B produces 100 mg by comparison, and they each receive a 50 mg pill of Agent X that has been shown to be an effective treatment for hyperhidrosis, then if Patient A has 50% reduction in sweating (which in her case would be a reduction by 100 mg of sweat) it would be expected that Patient B would have approximately a 50% reduction in sweating (which in her case would a reduction by 50 mg of sweat). This assumption enables the comparison of patients within a study despite different patients being enrolled in the study with different levels of baseline disease severity. This assumption essentially “normalizes” changes in disease state due to treatment by reference to each patient's own baseline of disease. This assumption not only enables the comparison of patients within a study despite different patients being enrolled in the study with different levels of baseline disease severity, but it also enables the comparison of results across studies of similar (e.g., one pill versus another) or different treatments (e.g., a pill versus an injectable treatment) for hyperhidrosis. The different treatments can be compared across studies by comparing the percent reductions in sweat for each treatment/study. See, for example, Naumann (2001), Heckmann (2005), and Lowe (2007) which used the percent reduction in produced sweat as a standard parameter for each of these clinical trials.